IRON COMPOUNDS. 21 



THE PHYSIOLOGICAL ROLE OF IRON COMPOUNDS. 



RELATION BETWEEN THE COLORING MATTER OF THE BLOOD AND OF 



THE LEAF. 



Iron compounds are indispensable for the production of the chloro- 

 phyll" of the plant and of the haemoglobin of the red blood corpuscles 

 of the higher animals. Without the former there is no assimilation 

 of carbonic acid, hence no synthesis of organic matter in the green 

 plant, and without the latter no respiration of the vertebrates, since 

 it is the haemoglobin that carries the molecular oxygen to the remotest 

 regions of the body. Although the chlorophyll itself does not con- 

 tain iron, haemoglobin contains it as an essential constituent of the 

 molecule. 



There is evidently a close relation between the coloring matter of 

 the leaf and that of the blood. The phylloporphyrin obtained from 

 chlorophyll by the action of alkalis shows almost the same spectrum 

 as the haematoporphyrin obtained from the haemoglobin of the blood. 

 Haematoporphyrin seems to correspond to a dioxyphylloporphyrin, 

 and both of these compounds appear to be derivatives of pyrrol. It 

 was especially the investigations of Nencki and of Tschirch that first 

 directed attention to the analogies between these two physiologically 

 important bodies. 



INFLUENCE OF IRON AND OTHER MINERAL NUTRIENTS ON THE FOR- 

 MATION OF CHLOROPHYLL. 



Iron is not the only requisite for the production of chlorophyll. 

 Other mineral nutrients are not less necessary, and above all only a 

 normal plastid can produce the green color with the aid of iron salts and 

 thus become a chloroplast; hence cases of imperfect plastids may occur, 

 e. g., where an increased supply of lime is required to produce normally 

 green leaves. A case where phosphoric acid was required in addition 

 to the iron to produce the chlorophyll was observed by the writer in 

 the case of an alga. Some threads of Spirogyra majuscula were placed 

 in 2 liters of distilled water, to which were added only 0.2 per mille 

 calcium nitrate and 0.02 per mille ammonium sulphate. When they 

 were placed in this very imperfect solution the filaments contained, in 

 all probability, some stored-up mineral matter, hence a moderate 

 further growth of the cells was not surprising. Besides, mineral 



«An observation on chlorophyll made by the writer may here be mentioned, as it 

 demonstrates beyond a doubt the great sensibility of this substance toward chemical 

 reagents. When Spirogyra threads are treated with moderately concentrated hydro- 

 chloric acid, they at once assume a yellowish color, but soon afterwards turn to a 

 bluish green, which points to two successive changes and indicates that in the prep- 

 aration of pure chlorophyll strong acids have to be avoided. Various discrepancies 

 in the observations of different authors may be traced to this circumstance. 



